The present invention relates to a process for measuring the ambiguous distance and to a pulse Doppler radar using such a process.
In a Doppler radar transmitting pulses at a repetition frequency f.sub.R the spectrum of the signal transmitted is composed of a principal line at the carrier frequency f.sub.o and of side lines situated on either side of the carrier frequency f.sub.o at intervals equal to the repetition frequency f.sub.R. Compared with the signal transmitted, the signal received has undergone a delay equal to the time taken for the signal transmitted to cover the radar-target-radar distance, and a frequency shift f.sub.d due to the Doppler effect. It therefore comprises a principal line at the frequency f.sub.o +f.sub.d and side lines separated by f.sub.R, the repetition frequency.
Some pulse Doppler radars have a distance ambiguity due to the fact that the delay on the signal received compared with the signal transmitted is only known with a modulo equal to the repetition period T.sub.R =1/f.sub.R. This is the case in particular if the pulse repetition frequency is high. This distance ambiguity can be eliminated by changing the repetition frequency. During an interval of time when the repetition frequency is constant, the radar can only measure the ambiguous distance. The present invention provides a process for measuring the ambiguous distance.
A known process for carrying out this measurement consists in splitting the reception window into two split gates of the same width, and in calculating the ratio ##EQU1## in which P.sub.1 and P.sub.2 are respectively the power of the output signal of the receiver corresponding to each of the two split gates.
This process has the following two disadvantages:
The characteristic obtained, (i.e. measurement of the ambiguous distance as a function of the ambiguous distance) is not linear around zero. PA1 The characteristic is limited as soon as the absolute value of the ambiguous distance exceeds the product of the speed of light multiplied by a quarter of the width of the pulse transmitted (saturation effect).
The present invention makes it possible to overcome the above disavantages and relates to a process for measuring the ambiguous distance.
One advantage of the present invention is that it gives a linear characteristic of the measurement of the ambiguous distance as a function of the ambiguous distance.
Another advantage of the present invention is that it makes measurement of the ambiguous distance always possible when the pulse received is not totally eclipsed.
Another advantage of the present invention is that it makes it possible, in the case of a formation of several targets, to obtain a linear measurement of the ambiguous distance over the entire reception window, for each of the targets, with an transmission form factor of less than 0.5.